Electric and hybrid electric vehicles use alternating current (AC) motor drives to provide torque to a motor shaft that drives the wheels of the vehicle. In practice, the amount of torque produced by the motor is directly related (although not perfectly proportional) to the amount current provided to the motor. Therefore, by regulating and precisely controlling the input current to the electric motor, the amount of torque produced by the electric motor may be more accurately controlled. However, in many systems, the input motor current is not directly controlled. For example, many electric motors are operated using pulse-width modulation (PWM) techniques in combination with an inverter (or another switched-mode power supply) to control the voltage across the motor windings, which in turn, produces the desired current in the motor.
In response to a requested torque (or commanded torque), conventional engine control systems determine a desired input motor current for producing the requested amount of torque and utilize a closed loop control system to control the current through the motor windings and thereby attempt to regulate the amount of torque produced the motor. One or more sensors are used to measure the actual motor current, which is then compared to the desired input motor current. Based on the outcome of the comparison, the PWM commands for the inverter are adjusted to increase and/or decrease the voltage across the motor windings, such that the actual measured motor current tracks the desired input motor current as closely as possible.
However, when a current sensor does not accurately reflect the motor current, these closed-loop control systems can no longer effectively control the motor. For example, without accurate motor current information, the control system may cause the motor to produce insufficient torque, excessive torque, or varying or oscillating amounts of torque. Consequently, the use and enjoyment of a vehicle is adversely affected when current sensor measurement errors occur or when the control system cannot adequately compensate for such errors.
Accordingly, it is desirable to provide a simple, reliable and cost effective solution for current estimation in electric or hybrid electric vehicles. Additionally, other desirable features and characteristics of the present invention will become apparent from the subsequent description taken in conjunction with the accompanying drawings and the foregoing technical field and background.